1. Field of the Invention
This invention relates generally to electronic test equipment, and more particularly to an electronic test probe for trouble shooting automotive DC electrical systems.
2. Description of the Prior Art
In trouble shooting automotive electrical systems, it is desirable to have an easy to use hand-held probe which includes both a prod member for making electrical contact to various points throughout the system under inspection and which also bears indicator means providing direct immediate indication of the signal being received at the prod member. The visual readout capability as an integral part of the probe, enables the operator to rapidly follow signals through complicated circuits without having to turn his head or attention therefrom by referring to a remotely located indicator or instrument panel to read the parameter being measured. It is also desirable for such a test probe to be designed such that an operator can rapidly and seqentially take any electrical measurements required in the trouble shooting procedure without, after initial set-up of the probe, having to be concerned with the relative polarities of the power supply connections energizing the probe circuits. While such probes must be highly reliable and designed so as not to fail over extended periods of use, they should be sufficiently inexpensive so as to be readily accessible by the unprofessional casual user.
Automotive test probes having one or more of these features are known in the prior art. However, the prior art test probes fail to satisfy all of the above-listed desirable features. Most prior art test probes employ a plurality of indicator lamps in a hand-held probe unit for indicating positive or negative voltage parameters being measured by a prod member. Such prior art apparatus has generally operated in a mode such that both positive and negative indicator lamps are normally illuminated, wherein one or the other is thereafter extinguished when a voltage parameter is received by the prod member. Such operation necessarily dictates that both of the indicator bulbs be illuminated throughout practically the entire test measurement procedure, even though during a majority of that time test measurements are not being directly taken, thus reducing the effective operative life of the bulbs. Further, the probe circuitry of such prior art devices has been configured such that the full measured voltage is typically applied across the appropriate indicator bulb, subjecting such bulbs to severe transient conditions, thus further reducing their operative life. To counteract these disadvantages, prior art devices have typically either used telephone circuit bulbs having generally low visibility to the user, or have used bulbs with higher power ratings, which have been proportionately more expensive.
Many prior art test probes have been operable to merely indicate the presence or absence of a voltage signal at the test prod, and are inoperable to indicate the relative magnitude of the measured signal. Further, some test probes have included self-contained batteries for energizing their test circuits, but such devices are generally limited in their trouble-shooting application and provide a nusuance in the maintenance and replacement of the batteries. Since an automotive storage battery is generally readily available when trouble shooting automotive electrical systems, the majority of test probes for such applications have provided for energization of the test probe circuits directly from the output terminals of the storage battery. Such test devices have, however, been limited in the type of measurements which can be sequentially taken during a trouble shooting procedure, and have required the user to switch the polarity of the storage battery connections to the test probe, before certain measurements could be taken.
The present invention overcomes the disadvantages and problems associated with prior art automotive DC type probes, by providing an inexpensive and easy to use test probe which incorporates unique circuit design for maximizing reliability and life of individual components therein. With the test probe of this invention, the user can continuously sequentially perform all test measurements required during an extended trouble shooting procedure, including measurements which require readings of relative magnitudes of measured signals, without ever having to alter or change the polarities of the supply connections energizing the probe circuits from a storage battery.
While particular probe housing and battery terminal connector configurations will be disclosed, it will be understood that other configurations could equally well be employed. Also, while specific reference voltage establishing circuits will be disclosed with respect to the preferred embodiments of this invention, it will be understood that other circuit arrangements could equally well be configured with the reliability, simplicity and cost constraints of this invention. Further, while specific component values will be disclosed with respect to the preferred embodiment circuit configurations, it is apparent that one could design operatively equivalent test probe circuits using different component values.